The embryonic chick cardiovascular system will be used to further substantiate the roles of hemodynamic alterations and/or impaired cardiac function, beta-adrenergic receptor hyperstimulation, and cyclic adenosine 3'5' monophosphate and/or calcium in the production of cardiovascular malformations. Compounds known to stimulate cardioselective beta-adrenoceptors have been shown to induce cardica and aortic arch anomalies in chick embryos in this laboratory. Theophylline, a compound that increases cardiac contractile force in mammals and chick embryos. Microcinematography, time-lapse microphotography, histology, electron microscopy, bioelectrical impedance cardiography, electrocardiography, gross morphology, dose response data and radioimmunoassay will be employed in search of valuable clues to mechanisms involved in abnormal cardiogenesis and/or aortic arch teratogenesis.